1. Field of the Invention
The present invention relates to a polarization diversity device and, more particularly, to a polarization diversity device for reducing fading effects during radio reception.
2. Description of the Related Art
Generally, fading occurs when a reception field intensity varies periodically due to interfering radio waves two or more different channels or by a change in condition of the received radio communication. Width of the fading (width change) reaches from nearly 0 dB to beyond 10 dB, and a cycle thereof reaches from one second to several hours.
Various methods have been used in the prior art to reduce a fading effect under such a fading environment. One of such methods is a diversity method which uses two antennas and selects one antenna at a certain time point. Such conventional diversity method, however, has the disadvantage of utilizing two antennas for reducing the fading effect. Accordingly, the conventional diversity method has additional disadvantages due to the use of two antennas, such as the cost of manufacture being considerably increased and the circuit being made complicated.
The use of polarization diversity is well known in the art for combating losses in different conditions. Polarization diversity consists of using two antennas with responsive orthogonal polarizations to receive or transmit the same signals. U.S. Pat. No. 4,186,347 to Milton H. Brockman, et al., and entitled Radio Frequency Arraying Method For Receivers describes the use of two antennas having polarized diversity for increasing signal-to-noise ratio of a receiving facility using power dividers and phase shifters. To overcome the deficiencies related to using two separate antennas, U.S. Pat. No. 5,499,033 entitled Polarization Diversity Antenna to Martin S. Smith contemplates the use of a single dual polarized flat plate antenna comprising separate horizontal and vertical flat plate antenna structures superimposed one on the other. Additonally, U.S. Pat. No. 4,410,891 to Daniel H. Schaubert, et al. entitled Microstrip Antenna With Polarization Diversity contemplates a single antenna element for constructed to provide complete polarization coverage with the necessity of using power dividers and phase shifters.